Vaccines are used to stimulate an immune response in an individual to provide protection against and/or treatment for a particular disease. Some vaccines include an antigen to induce the immune response. Some antigens elicit a strong immune response while other antigens elicit a weak immune response. A weak immune response to an antigen can be strengthened by including an adjuvant in the vaccine. Adjuvants come in many different forms, for example, aluminum salts, oil emulsions, sterile constituents of bacteria or other pathogens, cytokines, and so forth.
Cytokines are proteins made by cells that affect the behavior of other cells, and unlike many adjuvants, can modulate specific immune responses. One such cytokine is Interleukin-33 (IL-33). IL-33 is an endogenous signal or alarmin that alerts the immune system upon tissue injury or infection. In particular, full-length IL-33 is released into the extracellular space and activates its receptor ST2. Activation of ST2 leads to inflammatory and type 2 immune responses.
Vaccines are also administered in many different ways (e.g., injection, orally, etc.) into many different tissues (e.g., intramuscular, nasal, etc.). Not all delivery methods, however, are equal. Some delivery methods allow for greater compliance within a population of individuals while other delivery methods may affect immunogenicity and/or safety of the vaccine. Accordingly, a need remains in the art for the development of safe and more effective adjuvants that increase immune responses to the antigen.